1. Field of the Invention
This invention relates, in general, to electrostatic transfer in a reproduction apparatus, and more specifically, to a device for cleaning a transfer drum of such apparatus.
2. Description of the Prior Art
Cleaning devices for transfer drums in reproduction apparatus, such as electrographic copiers or printers, are well known. For example, color copiers presently available attach a sheet of paper to a transfer drum. The drum is rotated a plurality of times bringing a transfer surface of the sheet into transfer relationship with an electrophotographic imaging member. With each presentation of the transfer surface to the imaging member a different colored toner image is transferred to the transfer surface, generally under the urging of an electric field. Several color images are superposed in this manner forming a multicolor image on the transfer surface.
Inevitably, toner and paper fibers get on the external cylindrical surface of the transfer drum cleaning roller itself where they then transfer to the rear of the next cleaning sheet. Fur brush cleaners and web cleaners have been used commercially to clean the external cylindrical surface of transfer drums in such apparatus; see, for example, U.S. Pat. No. 3,819,263. Such cleaning devices are articulated from a position out of contact with the drum, when the apparatus is in a transfer mode, to a position in cleaning engagement with the drums, when the apparatus is in a cleaning mode. Fur brushes generally require vacuum or other fairly complex mechanism to get rid of the toner and also must be driven by a motor. Web cleaners are less expensive but the web itself must be indexed and the web must be changed periodically.
Transfer drums are also known which receive toner images directly to their external cylindrical surface without the interposition of a transfer sheet. In color apparatus, these drums receive more than one image in registration to their surface forming a multicolor image on the drum surface. The multicolor image is transferred to a transfer sheet either in the same nip as the original toner images were transferred or at a location remote from the original nip. Because of incomplete transfer to the transfer sheet, the external cylindrical surface of these drums generally must be cleaned between formation of each multicolor image.
Roller cleaners have been used commercially to clean reproduction apparatus transfer drums; see for example, U.S. Pat. No. 4,862,224 (issued Aug. 29, 1989, in the name of Ku). In its simplest form, a soft conductive rubber roller is allowed to roll with the transfer drum, an electrical bias is applied to such rubber roller to attract the toner to it from the transfer drum, and the softness of the rubber roller compared to the surface of the transfer drum cooperates with that bias to clean the drum. The roller itself passes into contact with a scraper blade which scrapes the toner into a disposing mechanism, for example, a housing or the like.
A problem which must be overcome in scraping toner from the cleaning roller of a device of the above type is that it is difficult to maintain the scraper blade in proper intimate association with the transfer drum. That is, the scraper blade can become loose in its holder, or can assume a wave-form shape due to uneven clamping forces in the holder. As such, the scraper blade is not maintained in uniform contact with the transfer drum. This results in incomplete cleaning of toner and other debris from the transfer roller. To rectify incomplete cleaning, it has been necessary in the past to change the scraper blade. However, due to the construction of the roller cleaner, replacement of the scraper blade has been difficult.